The number of countries involved in the search for the missing Malaysia Airlines plane grew to 26 over the weekend — a "significant diplomatic, technical and logistical challenge," according to Hussein Hishammuddin, Malaysia's minster of defense and acting minister of transport.

"Today, I can confirm that search and rescue operations in the northern and southern corridors have already begun," Hishammuddin said on Monday.

During the last 24 hours, the prime minister has spoken to the prime minister of Australia and the premier of China. Malaysia’s ministry of foreign affairs has sent diplomatic notes to all countries involved in the search and rescue operation. This includes two groups: first, countries in the search corridors; and second, countries from which we are seeking assistance and expertise.

Australia has increased its search efforts over the past 48 hours as new information revealed the plane may have travelled for more than seven hours after falling off the radar, placing its route in the direction of the coast of the country's western shore.

"In assuming overall responsibility for coordinating the search effort in the southern Indian Ocean, Australia is preparing to work with assets from a number of other countries, including surveillance aircraft from New Zealand and the United States,” Australian Prime Minister Tony Abbott said. The country has dedicated four AP-3C Orion maritime surveillance aircraft to survey the so-called "southern corridor" route where officials suspect the plane may have gone.

Along the alternative route, known as the "northern corridor," countries such as China and India stood at the ready as search-and-rescue teams prepared to analyze the sea, sky and ground along the plane's possible route. Indian newspapers and television shows questioned whether a major Indian city may have been the target of a botched Sept. 11-style attack, though no new evidence has arisen suggesting links to terrorism.

"I don't think we have gone that far," said Indian Foreign Minister Salman Khurshid.

Over the Bay of Bengal, a nine-person U.S. Navy crew aboard a P-8A Poseidon scoured 7,500 square miles of sea for any sign of the plane or its debris on Sunday. Nothing has been found thus far.

Meanwhile, French investigators have arrived in Kuala Lumpur to assist with the search. They are cautioning that this case is far different than an Air France jet that crashed into the Atlantic Ocean in 2009; then, they at least had distress signals to go by. The Malaysia Airlines plane disappeared without a peep.

As new reports surfaced that an in-plane communications system may have been disabled before the co-pilot's final signoff, some questioned whether his final words gave an ominous hint to ground control. Officials are refocusing their scrutiny on the plane’s pilot, Captain Zaharie Ahmad Shah, 53, and his first officer, Fariq Abdul Hamid, 27. Photos of the flight simulator that Shah constructed in his basement have already been posted online.

"Initial investigations indicate it was the co-pilot who basically spoke the last time it was recorded on tape," Malaysia Airlines CEO Ahmad Jauhari told a reporter who asked about the last words.

They came at 1:19 a.m., shortly after the Flight 370 left Malaysian airspace over the South China Sea. The last transmission from the on-board communications system had been received at 1:07 a.m.

So now CEO of airline says ACARS shut down sometime between 107am - 137am.ATC contact by co-pilot 119amTransponder off at 121am#MH370

Speaking to ground control, the co-pilot gave a rather casual sign-off that differed from standard radio procedures, which call for the speaker to read back instructions for contacting the next control center.

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